| accepts these headers based on ABNF grammar format and restricts them to a maximum of 10 server-vals. You must explicitly turn ON these headers for transparency. Additionally, if a header requires more than 10 server-vals in compliance with ABNF grammar, the header must convert to an unknown header using SMM. SIP provides a mechanism to represent common header field names in an abbreviated form. This may be useful when messages are too large to be carried on the transport available to it. A compact form may be substituted for the longer form of a header field name at any time without changing the semantics of the message. A header field name may appear in both long and short forms within the same message. A compact form of some common header field names is also defined for use when overall message size is an issue. Any headers marked with an alternate like: ' | ' indicates the long form or the short form of the header. In order to maintain backward capability, as of 4.1.6R0 and 4.2.4R0 releases, | 
